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Apparent transinhibition of peptide uptake in the scutellum of barley grain
Author(s) -
Sopanen Tuomas,
Sinervo Tuija,
Mikola Juhani
Publication year - 1985
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1985.tb02810.x
Subject(s) - glycylglycine , peptide , hordeum vulgare , alanine , proline , biochemistry , mixed inhibition , scutellum , glycine , chemistry , biology , amino acid , non competitive inhibition , biophysics , enzyme , botany , poaceae , endosperm
The uptake of glycylsarcosine (Gly‐Sar) into scutella separated from germinating grains of barley ( Hordeum vulgare L. cv. Himalaya) is inhibited by other peptides; in most cases the inhibition is not purely competitive but of a mixed type (simultaneous increase in the apparent K m and decrease in V max ) (Sopanen, T. 1979. FEBS Lett. 108: 447–450). The aim of the present experiments was to elucidate the mechanism of the mixed inhibition by studying how peptides already taken up into the cells affect the uptake of Gly‐Sar. When scutella were preincubated in the presence of various peptides, 11 of the 13 peptides tested inhibited the subsequent uptake of Gly‐Sar by 10 to 45%. The inhibition, studied in detail with leucylleucine and prolylproline, was due to a decrease in V max . The two peptides having no effect were glycylglycine and D‐alanyl‐L‐alanine which are the only peptides known to date acting as purely competitive inhibitors when present together with the substrate Gly‐Sar. Preincubation with leucine, proline and alanine was not inhibitory, although preincubation with the corresponding dipeptides was. This result, together with the demonstration of intact leucylleucine in the scutella after preincubation with leucylleucine, indicates that the inhibition was caused by the intact peptides. The results support the notion that in the mixed type inhibition the increase in the apparent K m is due to competition for the carrier at the outside of the membrane, while the decrease in V max is due to peptides taken up and binding to the carrier at the inside of the membrane.